Augmented reality imaging system

ABSTRACT

An optical system is presented for use in an augmented reality imaging system. The optical system comprises a light directing device, and a projecting optical device. The light directing device is configured for directing input light, including light indicative of an augmented image to be projected and input light indicative of a real image of an external scene, to propagate to an imaging plane. The projecting optical device has a fixed field of view and has a plurality of different focal parameters at different regions thereof corresponding to different vision zones within the field of view. The projecting optical device is configured to affect propagation of at least one of light indicative of the augmented image and light indicative of the real image, such that, for each of the different regions, interaction of a part of the light indicative of the augmented image and a part of the light indicative of the real image with said region of projecting optical device directs the parts of augmented image light and real image along a substantially common output propagation path, corresponding to the focal parameter of said region.

TECHNOLOGICAL FIELD AND BACKGROUND

The present invention is generally in the field of augmented realitytechniques, and relates to an optical system and method for projectinglight in augmented reality systems. In particular, such optical systemmay be incorporated within a see-through near-eye display, orhead-mounted display (e.g. helmet- or eyeglasses-mounted display), whichhas the capability of reflecting projected images as well as allowingthe user to see through it.

A near-eye display is a wearable device that creates a display in frontof a field of vision of a user. Near-eye displays include such maincomponents as an image generator and an optical combiner. The imagegenerator provides digitally reproduced images, e.g. utilizing a spatiallight modulator (SLM) or similar devices typically including a pixelmatrix which is imaged to infinity by a collimating lens and istransmitted into the eye of the viewer by reflecting or partiallyreflecting surface(s) acting as a combiner for, respectively,non-see-through and see-through applications. For an augmented realitydisplay, the optical combiner works to combine light from the externalworld and from the image generator into a single presentation of visualdata to the imaging optics and eyes.

A near-eye display presents image information to a viewer within viewingpupils (also referred to as “eyeboxes”), which when aligned with thepupils of the eyes of the viewer, produces virtual images within thefield of view of the viewer. Combiners, or waveguides, of near-eyedisplays convey image information toward the eyes of a viewer frompositions outside the field of view of the viewer.

Various example of such waveguides suitable for use in augmented realitysystems are described in the following patent publications, all assignedto the assignee of the present application: U.S. Pat. Nos. 8,098,439;7,643,214; 8,000,020; 7,724,442; 8,004,765; 7,577,326; 6,829,095;US2015138451; WO16075689; WO16103251; U.S. Pat. Nos. 9,513,481;9,551,880; 9,551,874. In such waveguides, light carrying an augmentedimage is guided by total internal reflection to a partially reflectivesurface from which it is reflected to a viewer.

GENERAL DESCRIPTION

There is a need in the art for a novel approach for configuring anoptical device for use in an augmented reality system. It should beunderstood that in an augmented reality system, a virtual image isaugmented onto the real scene image. Accordingly, in the augmentedreality system, implemented in a see-through near-eye display,high-quality images should be concurrently provided for both the realimage and virtual/augmented image within the entire field of view of thesystem, for differently distanced real and virtual objects.

In order to provide comfort to a viewer for observing both the augmentedand real images, in many cases either of these images or both are to bemodified. It is known to implement electronically controlled dynamiclenses, enabling the user to dynamically control the focus of the image.

The situation is different in a so-called “static” augmented realitysystem in a see-through near-eye display, namely the system having fixedoptical properties such as field of view, optical power/focalparameters' profile within the field of view of the system. The presentinvention provides for achieving the required comfort by improving theconcurrent appearance of both the augmented and real images to a viewerusing the so-called static optical system. To this end, the opticalsystem of the invention is configured such as to cause projected lightportions indicative of the augmented and real images, respectively, topropagate to the viewer's eyes (image plane) along a common optical pathfor far distanced objects virtual and real objects and a common opticalpath for closer distanced virtual and real objects. In this connection,it should be noted that, although in the description below, theinvention is exemplified as being used for applying a focal change inupper part and lower part of the field of view of the optical system,the principles of the invention are not limited to this specificexample, and the focal change can be applied to any otherpart(s)/section(s) across the field of view of the system.

In most cases, in the augmented reality systems, nothing needs to bedone with the real image of an external scene, i.e. far and closedistanced objects are to be presented to a viewer as they are. However,in some cases, the real image projection is to be performed in a waysimilar to that of a multi-focal lens (e.g. progressive lens), such thatboth the augmented image and the external world (real image) are focusedto infinity in the upper segment of the FOV where the real objects arefar and in the lower segment of the FOV where real objects are typicallynear. This requires modification of light indicative of the real imagebeing projected.

In most cases, the appearance of a virtual image, which is to beproperly augmented on the real scene image is to be improved. This isachieved by affecting/modifying convergence (focusing) of lightindicative of the augmented image being projected. The convergence oflight indicative of the augmented image may be affected prior to thislight interaction with a light combining surface, which combines outputpropagation paths of the augmented-image light and real image light,thus leaving the real-image light unaffected.

In some cases, the system configuration requires that theaugmented-image projection be affected just in front of the user's eyes,namely while in the combined projection path of both the augmented-imageand real-image light rays. Accordingly, this effect is to be compensatedfor the real-image appearance.

The present invention provides a novel optical system (at times referredto as image projector) for use in augmented reality system. The imageprojector of the invention is configured with a fixed field of view(FOV) and fixed profile of optical properties within said FOV, andaffects light propagation therethrough such that a virtual focal planeis created, which is slanted/tilted with respect to an optical axis ofthe image projector.

According to some embodiments of the invention, there is provided anoptical system for use in an augmented reality imaging system, theoptical system comprising:

a light directing device configured for directing input light, includinglight indicative of an augmented image being projected and input lightindicative of a real image of an external scene, to propagate in ageneral propagation direction to an imaging plane; and

a projecting optical device having a fixed field of view and having aplurality of different focal parameters at different regions thereofcorresponding to different vision zones within said field of view, theprojecting optical device being configured to affect propagation of atleast one of the light indicative of the augmented image, such that, foreach of said different regions, interaction of a part of said lightindicative of the augmented image and a part of said light indicative ofthe real image with said region directs the parts of the lightindicative of the augmented image and light indicative of the real imagealong a substantially common output path corresponding to the focalparameter of said region, thereby providing in-focus images in saidimaging plane for said parts of light indicative of the augmented imageand light indicative of the real image.

It should be understood that when speaking about augmented realityimaging system, such as see-through near-eye display or head-mounteddisplay, the term “imaging plane” actually refers to a so-called eyebox.The latter is a volume of space within which an effectively viewableimage is formed by an imaging system, representing a combination of exitpupil size and eye relief distance.

Generally, the light directing device is configured to define at leastone light combining surface located in optical paths of the input lightindicative of the augmented image and the input light indicative of thereal image for reflecting one of these lights and transmitting the otherto propagate towards the image plane. In the see-through near eyeaugmented reality systems, the light combining surface reflects theaugmented-image light and transmits the real-image light. In someembodiments, the light directing device includes a light-guiding opticalelement (LOE) which is transmitting for light from an external source,and is configured to guide light propagation thereinside(augmented-image light) to and from a light output surface. For example,such LOE may be configured to guide light therethrough by total internalreflection from inner major surfaces thereof and output light therefromby light interaction with one or more partially reflective ordiffractive surfaces, each serving as the above-described lightcombining surface for directing the augmented-image light and real-imagelight.

The different vision zones are defined by regions of the projectingoptical device, such that when the optical system is in use, theseregions are aligned with (intersected by) user's line of sight in itsdifferent angular orientations, when the user is moving his pupils toobserve differently distanced objects. For example, the projectingoptical device may define far and near vision regions with differentfocal parameters/optical power for far and near distanced objects(similar to bi-focal lens), or may have the optical power/focalparameters' profile similar to that of a progressive lens. Thus,generally, these regions of different focal parameters may beimplemented as discrete regions or as continuously varying focus acrossthe field of view.

In some embodiments, the projecting optical device comprises anaugmented image projecting unit located in an optical path of the inputlight indicative of the augmented image while propagating towards thelight directing device. In this case, the projecting optical device isconfigured for affecting propagation of the light indicative of theaugmented image being projected, while not affecting propagation of theinput light indicative of the real image of the scene.

The augmented image projecting unit may comprise at least one lenshaving the plurality of different focal parameters.

In some other embodiments, the projecting optical device comprises anaugmented image projecting unit and a real image projecting unit havingthe same field of view, and located in a spaced-apart relationship inoptical path of light emerging from the light directing device. In otherwords, in this configuration, the projecting optical device affects theaugmented-image light and the real-image light. Each of these projectingunits has the plurality of different focal parameters, which may beimplemented as discrete regions or as continuously varying focus acrossthe field of view. The augmented image projecting unit and the realimage projecting unit are configured in an opposite symmetric manner,such that the plurality of focal parameters of the real image projectingunit compensate effects of the plurality of different focal parametersof the augmented image projecting unit. The augmented image projectingunit and the real image projecting unit are accommodated (at fixedlocations) at opposite sides of the light directing device.

It should be understood that an augmented image projecting unit locatedat the output of the light directing unit actually interacts with(affects propagation of) both the light indicative of the augmentedimage and the light indicative of the real image. Therefore, for suchembodiments, the term “augmented image projecting unit” is used solelyin order to distinguish this unit from a “real image projecting unit”which interacts only with the light indicative of the real image; butthe configuration and function of the augmented image projecting unitshould be properly understood and interpreted.

Each of such units may comprise at least one lens, where the lenses ofthese units have similar optical properties (the plurality of differentfocal parameters) and are located in a spaced-apart substantiallyparallel planes along a common optical axis while being oriented in theopposite symmetric manner with respect to a plane of the light directingdevice. As a result, these units apply opposite optical effects to thelight passing therethrough.

In any of the above-described embodiments, the projecting optical devicecomprises at least one lens, having one of the following configurations:a bifocal lens, trifocal lens, continuously changing focal distance lens(progressive lens); which can be; realized as one of: refractive lens,diffractive lens, Fresnel lens or reflecting surface.

In some other embodiments of the invention, the optical system includesa light directing device and an optical projecting device, where each ofthese devices is a multi-unit assembly/device. More specifically, thelight directing device includes an array of at least two light directingunits, each being configured as described above, namely guidingaugmented-image light towards a light output surface (light combiningsurface) and transmitting the real-image light to interact with saidlight output surface; and the light projecting device includes an arrayof light projecting units. The configuration is such that all theseunits, i.e. light directing units and light projecting units are locatedin a spaced-apart relationship along a common axis, such that real-imagelight successively propagates through (interacts with) all these units.Moreover, each light directing unit is enclosed between two of the lightprojecting units.

In such multi-unit light directing device, each light directing unit isselectively operated. More specifically, each light directing unit maybe operated independently, i.e. may be associated with its own augmentedimage source; or all of them (or at least some of them) may beassociated with a common image source, which is configured to beselectively switchable to direct augmented-image light to one of thelight directing units.

Each of the light projecting units is configured (i.e. has opticalprofile) such that, depending on which one of the light directing unitsis in operation in an imaging session, the respective light projectingunits (i.e. those with which both the augmented-image light andreal-image light interact) affect light propagation therethrough suchthat interaction of the augmented-image light with the respective lightprojecting units provides a desired effect (focal distance change),while interaction of the real-image light with the respective lightprojecting units on its way through the system does not induce any focaldistance change.

The invention also provides an augmented reality system comprising anaugmented image source producing input light indicative of an augmentedimage to be projected to a viewer, and the above-described opticalsystem. The augmented image source may comprise an image generator and acollimating module, such that the input light received by the lightdirecting device is collimated light indicative of the augmented imageto be projected.

According to another broad aspect of the invention, it provides anoptical system for use in an augmented reality imaging system, theoptical system comprising:

a light-transmitting waveguide configured for receiving input lightindicative of an augmented image to be projected, guiding said inputlight indicative of the augmented image, and coupling said light out ofthe waveguide to propagate along an output path towards an imagingplane;

a projecting optical device comprising an augmented image projectingunit and a real image projecting unit, each unit having a fixed field ofview and a plurality of different focal parameters at different regionsthereof corresponding to different vision zones within said field ofview, the augmented image projecting unit and the real image projectingunit being located in spaced-apart substantially parallel planes along acommon optical axis at opposite sides of the light-transmittingwaveguide, and being configured in an opposite symmetric manner withrespect to the waveguide, such that said plurality of different focalparameters of the real image projecting unit compensate effects of saidplurality of different focal parameters of the augmented imageprojecting unit, such that interaction of said light indicative of theaugmented image and said light indicative of the real image with each ofsaid different regions directs said light indicative of the augmentedimage and said light indicative of the real image along a substantiallycommon output path, thereby providing in-focus images in said imagingplane for said light indicative of the augmented image and said lightindicative of the real image.

According to yet another broad aspect, the present invention provides anoptical system for use in an augmented reality imaging system, theoptical system comprising:

a light directing device comprising at least one light combining plateconfigured for directing input light indicative of an augmented image topropagate along an output path in a predetermined direction anddirecting input light indicative of a real image of a scene propagatingalong said output path;

a projecting optical device having a fixed field of view and a pluralityof different focal parameters at different regions thereof correspondingto different vision zones within said field of view, the projectingoptical device comprising an augmented image projecting unit located inan optical path of said input light indicative of the augmented imagewhile propagating towards the light directing device, such that when theoptical system is in use, user's line of sight in different angularorientations thereof intersect with said different regions therebyproviding in-focus viewing of differently distanced objects.

The invention, in its yet further aspect provides an optical system foruse in an augmented reality imaging system, the optical systemcomprising:

a light directing device comprising at least one light combining plateconfigured for directing input light indicative of an augmented image topropagate along an output path in a predetermined direction anddirecting input light indicative of a real image of a scene propagatingalong said output path;

a projecting optical device having a fixed field of view and a pluralityof different focal parameters at different regions thereof correspondingto different vision zones within said field of view, the optical devicecomprising a real image projecting unit located in an optical path ofthe light indicative of the real image propagating towards the lightdirecting device, which combines said light indicative of the real imagewith the light indicative of the augmented image being projected anddirects them along a common path to an imaging plane.

According to yet another broad aspect of the invention, it provides anoptical system for use in an augmented reality imaging system, theoptical system comprising:

a light directing device configured for directing input light, includinglight indicative of an augmented image to be projected and input lightindicative of a real image of an external scene, to propagate to animaging plane, wherein the light directing device comprises an array ofat least two light directing units located in a spaced-apartrelationship along an optical axis of the system, the light directingunits being configured to selectively involve one of them in an imagingsession; and

a projecting optical device having a fixed field of view and having aplurality of different focal parameters at different regions thereofcorresponding to different vision zones within said field of view, theprojecting optical device comprising a plurality of light projectingunits located in a spaced-apart relationship along the optical axis ofthe system such that each of the light directing units is enclosedbetween a pair of the light projecting units, providing that dependingon the selected light directing unit being involved in the imagingsession, one or more of the light projecting units are located in anoptical path of the light indicative of the real image propagatingtowards the selected light directing unit, and one or more of the otherlight projecting units are located at output of the selected lightdirecting unit and are in optical path of both the light indicative ofthe augmented image and the light indicative of the real image, whereinthe light projecting units are configured to induce a compensationoptical effect on the light indicative of the real image, such thatinteraction of a part of the light indicative of the augmented imagewith one or more regions of said one or more light projecting units,respectively, induces a desired effect of focal distance change on saidpart of the light indicative of augmented image, while interaction of apart of the light indicative of the real image with one or more regionsof said one or more of the other light projecting units induces saidcompensation optical effect on the part of the light indicative of thereal image, thus keeping a focal distance of said part of the lightindicative of the real image substantially unchanged.

The invention also provides an optical system for use in an augmentedreality imaging system, the optical system comprising:

a light directing device configured for directing input light, includinglight indicative of an augmented image to be projected and input lightindicative of a real image of an external scene, to propagate to animaging plane;

a projecting optical device having a fixed field of view and having aplurality of different focal parameters at different regions thereofcorresponding to different vision zones within said field of view, saidprojecting optical device comprising a light projecting unit located inoptical path of light indicative of the augmented image and lightindicative of the real image being output from the light directingdevice and propagating towards the image plane, said light projectingunit having a predetermined optical power profile defining saiddifferent focal parameters configured in accordance with an opticalpower profile of a personal multi-focal lens of an observer, configuredto induce a compensation optical effect on the light indicative of thereal image, such that, for each of the regions of the projecting opticaldevice, interaction of a part of the light indicative of the augmentedimage and light indicative of the real image with said region induces afocal change on the light, said focal change compensating a focal changeto be successively induced by the light interaction with an alignedregion of the multi-focal lens.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosedherein and to exemplify how it may be carried out in practice,embodiments will now be described, by way of non-limiting example only,with reference to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a light propagation scheme in awaveguide structure used in an head up display system;

FIGS. 2A and 2B exemplify an effect of appearance of an augmented imagein, respectively, conventional augmented reality system and thatutilizing the optical system of the present invention;

FIGS. 3A and 4A illustrate, by ways of a block diagram, two examples ofan augmented reality system utilizing the optical system of differentembodiments of the present invention, respectively;

FIGS. 3B and 4B illustrate more specifically the system configurationsof the embodiments of FIGS. 3A and 4A, respectively;

FIGS. 5 and 6 more specifically illustrate the light propagation schemesaffected by, respectively, the augmented image projecting unit and thereal image projecting unit in the system configuration of FIG. 4A;

FIG. 7 exemplify the light propagation scheme affected by the augmentedimage projecting unit and real image projecting unit in the systemconfiguration of FIG. 4A, where these units are implemented as bi-focallenses;

FIG. 8 illustrates the operation of a two eye display system withconvergence utilizing the optical systems of the embodiment of FIG. 4A;

FIG. 9 exemplifies FOVs for eye-box of a non-symmetric shape;

FIG. 10A exemplifies the use of the optical system of the embodiment ofFIG. 4A in the progressive near eye display designed to be used in frontof personal progressive lenses;

FIG. 10B illustrates yet another embodiment of the optical system of theinvention for use in augmented reality system designed to be used infront of personal progressive lenses;

FIG. 11 schematically illustrates the configuration and operation of theoptical system according to yet another embodiment of the invention,where the optical projecting device may include only the real imageprojecting unit;

FIG. 12 more specifically illustrates the light propagation schemeproduced by the real image projecting unit, in either one of theembodiments of FIG. 4A or FIG. 11 with various convergence of image fromboth eyes;

FIG. 13 more specifically illustrates the effect on light propagationproduced by the projecting optical device in the embodiment of FIG. 4Aor FIG. 10A;

FIGS. 14A to 14C exemplify the configurations of lenses in the augmentedimage and real image projecting units; and

FIG. 15 schematically illustrates yet another example of the projectingoptical device of the invention, in which both light directing deviceand light projecting device are configured as a multi-unit assembly.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention provides a novel optical system for use in an augmentedreality imaging system, e.g. see-through near-eye display, or head updisplay systems. In this connection, reference is first made to FIG. 1which schematically illustrates the general configuration andoperational principles of some known head up display systems utilizingoptical systems of the kind to which the present invention relates.

FIG. 1 illustrates a light propagation scheme in an optical system 100which includes a light-transmitting waveguide 20 (e.g. planar waveguide)configured as a light-guide optical element (LOE) or substrate to guidelight therethrough via total internal reflection (TIR). The waveguide 20has a light input region 21 (which is aligned with an output of anaugmented image source 5 (including an image generator 4 and possiblyalso a collimating module 6), and light directing interfaces 16 and 22arranged with proper orientation inside the waveguide.

As shown, light waves 18 indicative of the augmented image output fromthe augmented image source 5 and being properly collimated interact withthe reflective interface 16 which reflects these light waves such thatthey are trapped inside the planar waveguide substrate 20 by totalinternal reflection. After several reflections from the major lower andupper surfaces 26, 28 of the substrate 20, the trapped light waves reacha partially reflecting surface(s) 22, which couples the light out of thewaveguide to propagate in a general propagation direction towards apupil 25 of viewer's eye 24.

As shown in the figure, it is known to use in the optical device 100 anoptical element, such as a lens 82 which focuses augmented-image lightL_(aug) and real-image light L_(real) onto a prescribed focal plane andoptionally corrects other aberrations of the viewer's eye, e.g.astigmatism. Such optical system is described for example in theabove-indicated publications WO 2016/103251 assigned to the assignee ofthe present application.

Reference is now made to FIGS. 2A and 2B which schematically illustratean effect which unavoidably occurs in the conventional augmented realitysystems, such as system 100 illustrated in FIG. 1, either utilizing acorrecting lens 82 or not. FIG. 2A illustrates the virtual/augmentedimage as being presented to the user/viewer in the above-describedsystem 100 of FIG. 1. As can be seen, the image (text in the presentexample) as presented to the user appears as a “flat” image in the focalplane (or a conjugate plane) defined by the optical system 100.Accordingly, in such a flat image, all the letters (features) in thetext are of the same size and virtual distance, which is due to theconstant predetermined optical power of the optical system (e.g. definedby the collimating module).

FIG. 2B illustrates the augmented image of the same text in a differentpresentation which is desired in some augmented reality applications. Ascan be seen, the same originally flat image/text appears to be slantedwith respect to the optical axis of the system. As a result, theletter's size varies in the virtual image such that the letters(features) corresponding to near distanced objects appear larger thanthose of farer distanced objects. In the present example, the features'size varies gradually. In other words, larger letters in the augmentedtext image seem to appear at a closer virtual distance to the user andsmaller letters seem to appear at a farther virtual distance from theuser, despite of the fact that they all are actually of the samesize/scale and angular orientation (with respect to line of sight) inthe augmented image generated by the image source. Consequently, thedocument (augmented image) will be presented in front of the observer ina slanted plane, i.e. not perpendicular to the optical axis defined bythe augmented reality imaging system. The appearance of the augmentedimage is consistent with the focus and the convergence distance, as willbe described further below.

As will be described further below, the optical system of the presentinvention provides for achieving the above effect of the augmented imagepresentation/projection exemplified in FIG. 2B, while not affecting thepresentation/projection of the real image of the scene. It should alsobe understood that considering the specific not limiting example of FIG.2B, a change in a focal distance of the virtual object appearance may bein an opposite direction: (i) the larger letters in the augmented textimage seem to appear at a farther virtual distance to the user andsmaller letters seem to appear at a closer virtual distance from theuser, despite of the fact that they all are actually of the samesize/scale and angular orientation (with respect to line of sight) inthe augmented image generated by the image source; the letters/featuresmay be of different sizes at closer and farther distances, while theinduced focal change causes them to appear as if of the same size.

Generally, the optical system of the invention is aimed at improving theconcurrent appearance of both the augmented and real images to a viewer.This is achieved in the invention by configuring the optical system suchas to cause projected light portions indicative of the augmented andreal images, respectively, to propagate to the viewer's eyes (imageplane) along common optical path(s). For example, augmented and realimages of near distanced objects propagate along a common projectionpath (i.e. the same convergence/same focal distance), and augmented andreal images of far distanced objects propagate along a common projectionpath.

To this end, the optical system of the invention includes an additionalspecifically designed projecting optical device. In some embodiments ofthe invention, the projecting optical device is configured to apply achange of optical power onto the augmented image while avoiding suchchange in the real image being projected. In some other embodiments, theprojecting optical device is configured to apply optical power changesonto both the augmented image and the real image such that, in the imageplane, the augmented image is modified while the real image ismaintained. In yet further embodiments, the optical system of theinvention is configured to affect only the light indicative of the realimage. This way both the virtual image and the external world arefocused to infinity in the far vision zone (upper FOV) where realobjects are far and in the near vision zone (lower FOV) where realobjects are typically near.

Reference is made to FIGS. 3A and 4A which illustrate, by way of blockdiagrams, two embodiments of an imaging system 200 for use in augmentedreality applications, utilizing an optical system 202 of the invention.To facilitate understanding, the same reference numbers are used foridentifying components that are common in all the examples.

Generally, the augmented reality imaging system 200 includes such mainparts (functional and structural parts) as an augmented image source205, a light directing device 210, and a projecting optical device 240configured and operable according to the invention. Common for all theconfigurations of system 200 is that the light directing device 210 isconfigured for directing input light, L_(aug), indicative of anaugmented image which is to be projected and input light, L_(real),indicative of a real image of an external scene, to propagate in ageneral propagation direction to an imaging plane (i.e. to viewer'seyes). Such a light directing device 210 may have any suitableconfiguration defining one or more beam combining surfaces (e.g.partially reflective and/or diffractive surfaces), each forreflecting/diffracting augmented-image light, L_(aug), and transmittingreal-image light, L_(real), to the imaging plane.

The projecting optical device 240 of the present invention has a fixedfield of view (FOV) and has a plurality of different focal parameters atdifferent regions of the device corresponding to different vision zones(at least first and second vision zones) within the FOV. Typically, suchat least first and second vision zones are constituted by at least farand near vision zones.

It should be understood that, for the purposes of the presentapplication, different vision zones are physical zones/regions of thedevice 240 corresponding to different focal parameters thereof in itsFOV. These regions of the device 240 are regions of intersection withthe observer/viewer's line of sight at different orientations thereof,when the observer/viewer is moving his pupils to observe differentlydistanced objects.

The projecting optical device 240 is configured such that each focalparameter thereof (corresponding region/zone) provides in-focus images,in the imaging plane IP, for the augmented-image light, L_(aug). As forthe real image of the scene, it is not affected by the projectingoptical device 240, and therefore is observed by the viewer based in theviewer's vision. As will be exemplified further below, the viewer may ormay not use his spectacles or contact lenses, and his vision is thusdefined accordingly. In other words, each focal parameter of the device240, and a respective zone/region of the device, defines a differentfocus for the augmented image. Generally, the projecting optical device240 is configured to affect light, L_(aug), indicative of the augmentedimage. Thus, for example, images of far and near distanced objects inthe augmented image are affected by respective different focalparameters (e.g. optical power) of the projecting optical device 240.

Referring to the embodiment of FIG. 3A, the projecting optical device240 comprises an augmented image projecting unit 240A located in anoptical path OP₁ of light L_(aug) propagating from the augmented imagesource 205 towards the light directing device 210. Accordingly, theprojecting optical device 240 affects only propagation of theaugmented-image light L_(aug) prior to its interaction with the lightdirecting device 210, while propagation of the real-image light L_(real)remains unchanged. Thus, for example, the slanted augmented image may beproduced as exemplified in FIG. 2B, while the real-world scene remainsunaffected by the device 202.

As indicated above, the projecting optical device 240 is configured tohave a plurality of different focal parameters across its field of view.These different focal parameters are associated with correspondingdifferent vision zones which are different regions of the projectingoptical device 240, which, when the system is in use (worn by viewer),are aligned with different angular orientations of the user's line ofsight when observing differently distanced objects.

Thus, collimated light L_(aug) indicative of augmented image, created bythe image source 205, interacts with (e.g. passes through) the augmentedimage projecting unit 240A at a certain region/zone thereof andundergoes respective focusing/convergence (defined by the focalparameter of said certain region/zone), and is then reflected by thepartially reflective surface (light combining surface) of the lightdirecting device 210 towards the projecting path CP to be focused on theimaging plane IP (viewer's eyes or eyebox). Concurrently, the real-imagelight L_(real) propagating along path CP interacts with (e.g. passesthrough) the partially reflective surface of the light directing device210 without being changed and continues to propagate in its originalprojecting path CP to be focused on the imaging plane IP (viewer'seyes).

It should be understood that, generally, the propagation paths of lightparts L_(aug) and L_(real) are combined into the common outputprojecting path CP if said propagation paths of light parts L_(aug) andL_(real) correspond to the same focal distances. Thus, in the specificconfiguration of the projecting optical device 240 having only augmentedimage projecting unit 240A, as exemplified in FIG. 3A, the focaldistance of the augmented-image light L_(aug) is affected at theinteraction zone with the augmented image projecting unit 240A to beproperly modified. The operation of such augmented image projecting unit240A will be described more specifically further below with reference toFIG. 3B.

Generally, common for all the embodiments of the invention, theprojecting optical device 240 may include one or more lenses, e.g. abifocal lens, trifocal lens, continuously changing focal distance lens(progressive lens), and/or any other optical device or assembly havingvarying focal parameters within its field of view. As a virtual objectmoves from an upper section of the FOV of the projecting optical deviceto a lower section of the FOV, its focal distance changes and theconvergence of augmented image light rays changes accordingly. In theembodiment of FIG. 4A, the projecting optical device 240 is a two-partdevice including an augmented image projecting unit 240B and a realimage projecting unit 240C accommodated at opposite sides, respectively,of the light directing device 210 in a spaced-apart parallel planesalong a common optical axis. Each of the augmented image projecting unit240B and the real image projecting unit 240C has the same fixed field ofview FOV. The augmented image projecting unit 240B is accommodated atthe front side of the light directing device 210 and the real imageprojecting optical unit 240C is accommodated at the back side of thelight directing device 210 with respect to the imaging plane.Consequently, real image projecting unit 240C is located at the opticalpath of real-image light L_(real), while the augmented image projectingunit 240B is located at the optical path of both real-image lightL_(real) and augmented-image light L_(aug). The arrangement of the lightdirecting device 210 and the projecting optical unit 240 is “static”, inthe meaning that the optical properties of this arrangement are fixed(i.e. field of view, optical power/focal profile across the FOV).

As described above, the light directing device 210 may have any suitableconfiguration having at least one beam combining surface (partiallyreflective/diffractive surface) for directing the augmented- andreal-image light parts incident thereon. For example, in the embodimentof FIG. 4A, the light directing device 210 is configured as an opticallytransmitting light-guiding optical element LOE having fully reflectinginner major surfaces for directing/guiding augmented-image light L_(aug)by total internal reflection and at least one partially-reflectingsurface for reflecting light L_(aug) towards the projecting path, andbeing transmitting for the external light L_(real) to thereby transmitthe real-image L_(real) towards the viewer.

The need for the augmented image projecting unit 240B (as well as unit240A described above with reference to FIG. 3A) may be associated withthe need for the “slanted” effect described above with reference toFIGS. 2A-2B. However, in the configuration of the augmented imageprojecting unit 240B being in the output path of the augmented-imagelight L_(aug), such augmented image projecting unit 240B unavoidablyaffects also the real-image light L_(real). To this, the real imageprojecting unit 240C is provided and is configured to compensate theeffect of augmented image projecting unit 240B on the real-image lightL_(real).

More specifically, the augmented image projecting unit 240B and the realimage projecting unit 240C have the same FOV. Each of the augmentedimage projecting unit 240B and the real image projecting unit 240C isconfigured to have a plurality of different focal parameterscorresponding to different regions/zones thereof within the field ofview, and the units 240B and 240C are aligned in an opposite symmetricmanner with respect to a plane of the light directing device 210. Thismeans that optical power profile across the FOV (i.e. different regionshaving different focal parameters) of the augmented image projectingunit 240B is aligned in an opposite symmetric manner with the opticalpower profile of the real image projecting unit 240C. Such an alignmentresults in that real-image light L_(real) while propagating in itsoriginal direction passes through unit 240C where it undergoes focalmodification (in case projecting unit 240B applies defocusing, theprojecting unit 240C applies a corresponding focusing effect) that willthen be compensated by the real-image light L_(real) passage through theaugmented projecting unit 240B, which applies the effective(non-compensated) focal modification to the augmented-image lightL_(aug). Thus, the real image projecting unit 240C is utilized here as acompensating optical unit nullifying the optical effects of theaugmented image projecting unit 240B on light L_(real).

For example, the real and augmented image projecting units 240B and 240Cmay include progressive lenses (continuously varying focus across theFOV of the lens) which are aligned in an opposite symmetric manner asfollows: One of these lenses may be a progressive lens with continuouslyincreasing optical power from the lower segment of the lens, i.e. lowersection of the FOV (typically used for observing near-distanced objects)towards the upper segment of the lens, i.e. upper section of the FOV(typically used for observing far-distanced objects), and the other lenswith the same FOV is a progressive lens with continuously decreasingoptical power from the lower segment of the lens towards the uppersegment of the lens.

Referring now to FIG. 3B, operation of the system 200 of the embodimentof FIG. 3A is more specifically illustrated. In this embodiment, theprojecting optical device 240 includes only the augmented imageprojecting unit 240A located in optical path OP₁ of augmented-imagelight L_(aug) propagating towards the light directing device. Inputaugmented-image light L_(aug) from the image source 205 interacts with(e.g. passes through) a region of the augmented image projecting unit240A, which has certain fixed FOV and has different focal parameters atdifferent regions thereof. In the present not limiting example, theaugmented image projecting unit 240A has a lens with continuouslyvarying focus, e.g. progressive lens. As indicated above, the principlesof the invention are limited neither to the use of progressive lens norto any other configuration of continuously varying focus. Theconvergence of the augmented-image light L_(aug) propagation is modifiedby interaction with the region of the lens in accordance with the focalparameter at said region. The so-modified augmented-image light L_(aug)propagating with said convergence is incident onto the light combiningsurface of the light directing device 210, which directs this light tothe user's eyes (image plane). Thus, the augmented-image lightinteraction with each of different regions of the lens 240A havingdifferent focal parameter provides appearance of the respectiveaugmented object/feature at a different virtual distance from the imageplane, presenting virtual object/feature located closer or farer fromthe viewer.

As shown in the figure, the modification of the convergence of theaugmented-image light L_(aug) by interaction thereof with the differentregions of the lens having different focal parameters provides differentappearance of the virtual object. In the present example, such differentappearance is exemplified as appearance of the close and far distancedobjects NO and FO, respectively, as being observed by the user.

As shown in FIG. 3B, the observer is looking through the light directingdevice 210 of the near eye display 200 and sees augmented-image lightfrom virtual objects FO and NO. The augmented-image light passes throughthe lens 240A that changes the focus of the virtual image differentlyacross the lens. Augmented image light interacting with a segment of thelens 240A having minimal negative optical power, provides the virtualobject appearance as the far distanced object FO (for example at 6meters). The augmented-image light interacting with a segment of theunit (e.g. lens) 240A having stronger negative optical power providesthe virtual object appearance as the near distanced object NO (forexample at 1 meter). A continuous focal change of the unit 240Agenerates continuous change in the distance of the appearance of virtualobjects along the virtual focal plane FP.

Considering the example of continuously varying focus of the projectingoptical device, it creates a virtual focal plane FP. In this connection,it should be understood that, generally, and this is common for all theembodiment of the invention, a virtual focal profile may or may not becontinuous, e.g. it may be not continuous for a case of discrete regionsof different focal parameters across the projecting optical device. Inother words, the shape of the virtual focal profile corresponds to thefocal/optical power profile across the FOV of the projecting opticaldevice.

As also shown in the figure, the real-image light L_(real) propagatingfrom a real far object RO (for example 6 m), passes through the lightcombining surface of the light directing device 210 into the viewer'seye. Thus, in this example, the progressive lens 240A is introduced inthe optical path of the augmented-image light L_(aug) only, while thelight L_(real) from the real ‘world’ is not affected by the optics ofthe system.

It should be noted that, generally and common for all the embodiments,the implementation of the projecting optical device 240 into the system200 can be done by modification of the system optics, by introducing thedevice 240 (or one or more of its lenses) internally, or by modificationof the surface of the light directing device 210 (with minimaldistortion to the ‘world’). This will be described further below.

Thus, the projecting optical device 240A provides that theaugmented-image light portions, having convergences corresponding to thenear and far distanced virtual objects, are coupled out of the lightdirecting unit 210, along different projecting paths CP_(N) and CP_(F)which are common paths for the real image light originated at near andfar distanced real objects RO.

Referring to FIG. 4B, there is more specifically illustrated an exampleof the operation of the system of the embodiment of FIG. 4A, where theprojecting optical unit 240 includes an augmented image projecting unit240B and a real image projecting unit 240C. The augmented imageprojecting unit 240B is located in the optical path of both theaugmented-image light L_(aug) and the real-image light L_(real) beingoutput from the light directing device 210. The light directing device210 may be a light-transmitting waveguide guiding input augmented-imagelight L_(aug) by total internal reflection from its major surfaces (asshown in FIG. 1) and coupling it out by reflection from partiallyreflective surface. This is a light combining surface which transmitsthe real-image light L_(real). The real-image projecting unit 240C islocated in the optical path of real image light L_(real).

In this specific but not limiting example, the projecting units 240B and240C are in the form of opposite symmetric progressive lenses. Asdescribed above, it should be understood that, generally, the projectingunits have opposite symmetric focal/optical power profiles across theidentical fields of view, and these profiles may correspond tocontinuous variation of focus or discrete regions of different foci.

The observer is looking through the optical system 202 of a near eyedisplay system 200 and sees light from virtual objects, being far andnear distanced objects FO and NO in this example. To this end, theaugmented image projecting unit 240B (e.g. progressive lens) providesthat interaction of light L_(aug) and light L_(real) with the sameregion of the lens induces respective convergence on both of these lightportions. More specifically, the upper segment of the lens 240B (theupper section of the FOV) applies minimal negative optical power to theinteracting light, and accordingly the respective virtual image appearsto originate from far distanced object FO (for example at 6 meters). Thelower segment of the lens 240B (lower section of the FOV) introducesstronger negative optical power to the virtual image light, and thus thevirtual image will appear to originate from a near distanced object NO(for example at 1 meter). A continuous focal change of the lens 240Bwould generate continuous change in virtual focal plane FO. As describedabove, generally, the shape of the virtual focal profile corresponds tothe focal/optical power profile across the FOV of the projecting opticaldevice 240.

In this configuration, the real image light experiences the same focalchange (convergence change) by the augmented projecting unit 240B as theaugmented image light. However, such change is not needed for the realimage light. Therefore, the compensating real image projecting unit 240Cis provided being configured as described above. The real imageassociated progressive lens 240C is placed adjacent and on the oppositeside of light directing device 210 and is designed to have the oppositeoptical power profile of lens 240B. This way real ‘world’ objects willnot be affected by the system.

Reference is made to FIGS. 5 and 6 which more specifically illustratethe light propagation schemes affected by, respectively, the augmentedimage projecting unit and the real image projecting unit in the systemconfiguration of FIG. 4A.

As shown in FIG. 5, the waveguide of the light directing device 210outputs parallel light beams of the augmented image light L_(aug) foreach of two virtual images associated with objects NO and FO. As thislight passes the augmented image projecting unit, which is a progressivediverging lens 240B in this example, the light at different interactionlocations/regions of the lens 240B experiences different amount ofdivergence. Consequently, the two virtual objects FO and NO appear to beat different virtual distances. Thus, the so modified augmented imagelight rays arrive at the image plane, i.e. the location in space whereobserver eye will experience the designed performance. It should benoted that points FO and NO are only an example, while actually acontinuous virtual focal plane or any other discrete focal profile (of abifocal lens for example) can be created by the augmented imageprojecting unit 240B. The orientation of the virtual focal profile canbe other than top down. It can also be side oriented.

The optical scheme for the real image light propagation is shown in FIG.6. The light rays from real far and near objects RO_(F) and RO_(N) areincident on real image projecting unit 240C (varying focal lens). Thedifferent regions of the lens 240C having different focal parameters,with which the far- and near-object associated light rays interact,apply respective different focal changes on these light rays, which thenpass through the waveguide 210. This way the real image light rays forthe predefined distance RO_(N) and RO_(F) and the augmented image lightrays emerging from the waveguide 210 are all collimated (focused toinfinity), and thereby correlated. Although not specifically shown inthe figure, it should be understood that all rays, those of real-imageand augmented-image light may then pass through the lens 240B togenerate the virtual image plane.

FIG. 7 exemplifies the operation of the optical system of the inventionutilizing a bifocal configuration of the projecting optical device 240including the augmented image projecting unit (bifocal lens) 240B andreal image projecting unit (opposite bifocal lens) 240C configured andarranged as described above. As shown, in this configuration the focalprofile FP is in the form of discrete focal distances/positions FP_(F)and FP_(N) to generate distinct two separate virtual images. The uppersection of the FOV generates focal position FP_(F) and the lower sectiongenerates focal position FP_(N). In a similar way, trifocal lenses, aswell as any other discrete focal values' lenses can be used generatingcorresponding discrete-values focal profile.

FIG. 8 illustrates, in a self-explanatory manner the optical system 202configurations for use in a two-eye display system. The system 202includes two similar units 202A and 202B. Each such unit is configuredas described above implementing the embodiment of FIG. 4A. It should,however, be understood that the embodiment of FIG. 3A can be used, aswell as another embodiment described below with reference to FIG. 11 canbe used.

It should be understood that the projecting optical devices 240 in theunits 202A and 202B are configured in opposite symmetric manner withrespect to a central line CL between them parallel to their opticalaxes. This provides that, for each focal parameter, virtual objectscreated by the units 202A and 202B coincide in space. This isexemplified in the figure for virtual objects NO and FO. The progressivechange in focal distances of virtual objects is accompanied bycontinuous change in convergence of the augmented image light rays beingoutput of the augmented image projecting unit. It should be noted that,in some cases, the convergence is designed (i.e. the respective lensesare configured) to be less then nominal for focus in order to maintainmargins for different eye distance of observers.

FIG. 9 shows some examples for the shape/geometry of the elements of theoptical system 202 in the augmented reality applications. As shown, theeye boxes (for left and right eyes) have an opposite symmetric shapeswith respect to the central line CL between them which in thisillustration is perpendicular to their optical axes. Also, each of theseoptical elements can be of a non-symmetric shape, because short rangeobservation mostly utilizes narrower FOV and eye tend to converge. Asalso shown in the figure, the same is relevant for a two-eye single eyebox, where the FOV can be arranged as ‘portrait’.

Reference is made to FIG. 10A, exemplifying the use of the opticalsystem of the invention in front of personal progressive lenses (knownin spectacles market) used by the observer. In this embodiment, thepersonal progressive lens 50 is closer than the optical system 202, i.e.is located downstream of the optical system 202 with respect to thelight propagation to the user's eye. In the present non-limitingexample, where the system has general configuration of FIG. 4A, theprogressive lens 50 is located closer than the augmented imageprojecting unit 240B. Generally, the optical system of the invention canbe conveniently used by progressive spectacle users. In two eyeconfiguration, the convergence of the augmented image light rays can beperformed according to the focal profile of personal progressive lens50. However, since progressive spectacles introduce minimal convergencebetween both eyes or none at all (thereby generatingaccommodation-convergence inconsistency especially at close distance),the induced convergence (modification) of the virtual image light raysaccording to the present invention can be set to minimal or none at all.Thereby, the convergence of the virtual image light rays is set togenerate accommodation-convergence consistency.

Referring to FIG. 10B, there is schematically illustrated optical system202 of the invention having a somewhat different configuration, beingconfigured to augmented reality system which is to be used by anobserver having personal multifocal spectacles 50. In this embodiment,the system 202 includes a light directing unit 210, and a projectingoptical device including only an augmented image projecting unit 240Blocated at the output of the light directing unit 210. Suchconfiguration might be advantageous for the case where the observerprefers to use the near eye display while the virtual image as well asthe ‘world’ are focused to infinity all across the FOV without the needto take of his spectacles. This is because in most cases spectacles alsocorrect aberrations. In this embodiment, the augmented image projectingunit (e.g. multi-focal lens) 240B is configured to cancel/nullify theoptical effect of progressive focus (generally, focal change) of thespectacles 50. Thus, the light projecting unit 240B has a predeterminedoptical power profile (defining the different focal parameters (acrossthe FOV) configured in accordance with the predetermined optical powerprofile of a personal multi-focal lens of an observer, to be oppositelysymmetric with respect to the optical axis of the system. Hence, foreach of the regions of the unit 240B, interaction of a part of theaugmented-image light and real-image light with this region induces afocal change on the interacting light, and this focal change compensatesfor a focal change which is successively induced by the lightinteraction with an aligned region of the multi-focal lens 50.

Reference is now made to FIG. 11 illustrating schematically an exampleof configuration and operation of an optical system 202 according to yetanother embodiment of the present invention. In this embodiment, thesystem includes a light directing device 210 defining at least one lightcombining surface/plate for reflecting/diffracting and transmittingrespectively augmented image light and real image light; and aprojecting optical device 240 which may include only real imageprojecting unit 240C. As described above, in some cases, the real imageprojection is to be performed similar to that of a multi-focal lens(e.g. progressive lens), such that both the augmented image and theexternal world are focused to infinity in the upper segment/section ofthe FOV where the real objects are far RO_(F) and in the lowersegment/section of the FOV where real objects are typically near RO_(N).This requires modification of light indicative of the real image beingprojected. In this configuration the observer sees the real and thevirtual images focused to infinity

FIG. 12 more specifically illustrates the light propagation schemeproduced by the optical systems of the invention exemplified in FIG. 11.It should be noted that the variable compensation for real-image lightconvergence across the FOV might be difficult to achieve in progressivelenses. Element RO represent far-distanced real object that is imaged byprogressive lens. The light rays L_(real) (solid lines) are parallel forevery eye related propagation path, but are not parallel between theeyes. A virtual image can be made electronically to have required lightpattern (represented as dashed lines). This is convenient when observingsimultaneously real and virtual objects. However, when observing virtualimage only it will be more convenient to have convergence to fit theaccommodation as presented by the dot-dash lines.

FIG. 13 schematically illustrates the advantageous feature of theoptical system of the invention. It should be understood that althoughthis is exemplified with respect to the optical system configuration ofFIGS. 4A and 4B, the same is true also for all the systemconfigurations, e.g. the system configurations of the above-describedFIGS. 3A-3B and 11, as well as the example described below withreference to FIG. 15. The observer, when using the near-eye displaysystem incorporating the optical system of the invention, is moving hishead with respect to the display system, as depicted by arrows 75.Accordingly, the virtual focal plane FP is being the path shown by arrow75. However, the virtual image can be set electronically to maintainrelative orientation in space, and appear to move up and further away indirection 77 along the focal plane FP. The system is configured toenable the user to change focus or virtual distance as required.Alternatively, the user can move the virtual object up in the field ofview without the head movement. This will have the same result: theobject will appear to move up and away along arrow 77. Generally, bothof these methods can be used by the observer to change object distanceand correlate it with real objects distance.

Reference is made to FIGS. 14A to 14C exemplifying some geometricalfeatures of the projecting optical device, e.g. progressive lens(es).The design of a multifocal lens (e.g. progressive lens) is well knownmethodology. However, for the purposes of the present application, themultifocal lens should preferably occupy a minimal volume of the opticalsystem. This can be achieved if the lens back surface 80 is designed tobe conformal with the adjacent outer surface of the light directingdevice (waveguide) 210. In most cases, this is a flat plane (asexemplified in FIGS. 14A-14B). For best optical performance, theopposite lens should also be adjacent and have a conformal back surface82. This surface can be attached to the waveguide 210 as long as itmaintains total internal reflection within the waveguide. Thesefeatures, as well as various examples of the manufacturing technique toachieve these features, are described in the above-indicated WO2016/103251 assigned to the assignee of the present application and alsoin a co-pending application No. PCT/2016/050523, both being incorporatedherein by reference with respect to this aspect of the invention.

According to the present invention, the shape of surfaces 84 and 86 canbe modified to generate the required progressive optical power. Thedesign of these shapes may be based on weighted average.

As shown in FIG. 14C, the surface of the lens by which it faces thewaveguide may not be planar. This is exemplified in the figure forsurface 82′ of one of the lenses. However, it should be understood thatthis feature can be used in any one of the above-described embodiments,for one or more of the lenses.

The method of optimization for the shape of the facing surfaces of thelenses can include various parameters, similar to that performed inprogressive lens design for spectacles. The basic approach for derivingthe outer surface of the lens is hereby described. However, it should beunderstood that other known suitable methods can be used.

According to the basic approach, the following parameters are used: rbeing the position on lens surface; R being the position on object realspace to be collimated on the virtual focal plane FP; P being theheight/position of lens surface designed to create wave-front from pointR correlating wave-front from waveguide (plane-wave in most cases), andcan be derived using optical simulation software; f being the weightingfunction depending on various parameters such as position of eye-box 90constituting the eye pupil (for example rays outside eye-box are of nosignificance).

The profile P(r) of the lens surface 84 is therefore averaged:

${P(r)} = \frac{\int{{P( {r,R} )} \times {f( {r,R} )} \times {dR}}}{\int{{f( {r,R} )} \times {dR}}}$A more complex iteration can be used to optimize lens surfaces such assurfaces 86 with 84. All the surfaces/interfaces of the projectingoptical device can also me optimized (e.g. surfaces 80, 82 (or 82′), 84and 86).

As further exemplified in FIG. 14B, the optical lens to be used as theprojecting optical unit in the system of the invention may be is basedon Fresnel lens. As sown in the figure, surfaces 186 and 184 of suchlens have same optical properties as those of surface 86 and 84respectively in the above example of FIG. 14A. As known, the use ofFresnel lens provides for reducing weight and size of the opticalsystem.

FIG. 15 schematically illustrates a projecting optical device 240configured according to yet another example of the invention. The device240 of this example is configured generally similar to the embodiment ofFIG. 4A, namely includes a light directing device 210 and imageprojecting device 240 in the optical path of both the augmented imagelight and the real image light. However, in this example, the lightdirecting device 210 and the image projecting device 240 are configuredas multi-unit devices/assemblies. More specifically, the light directingdevice 210 includes an array (generally at least two light directingunits)—three such light directing units 210 a, 210 b, 210 c being shownin the present example; and the light projecting device 240 includes anarray of light projecting units—units 240B′, 240B″, 240B′″, 240C in thepresent example. It should be understood that light projecting unit 240Cis the only one which interacts only with the real-image light and doesnot interact with the augmented image light. Each light directing unitin the array is configured as described above, namely for guiding inputaugmented-image light towards a light output surface (light combiningsurface) and transmitting the real-image light to interact with thelight output surface. The light directing units and light projectingunits are located in a spaced-apart relationship along a common axis(optical axis of the system). Each light directing unit (generally atleast one or at least some of them) is enclosed between two of the lightprojecting units. As shown in the figure, light directing unit 210 a islocated between light projecting units 240C and 240B′; light directingunit 210 b is located between light projecting units 240B′ and 240B″;light directing unit 210 c is located between light projecting units240B″ and 240B′″.

Hence, the real-image light successively propagates through (interactswith) all these units. As for the light directing units, each of them isselectively operated. More specifically, each light directing unit maybe operated independently: Each light directing unit may be associatedwith its own augmented image source, in which case the multiple imagesources may be selectively operated one-by-one, or at least some of themor all of them are operated concurrently. Alternatively, at least someof the light directing units or all of them may be associated with acommon image source. In the latter case, the common image source isselectively switchable between different operational modes to directaugmented-image light to different one or more of the light directingunits. The selection of the light directing unit and/or image source tobe operated in a certain imaging session can be implemented sequentially(the system scans the light directing units and injects the appropriateaugmented image to each one); and/or using an eye tracker based system(the system identifies, using an eye tracker, where the observer islooking (i.e. orientation of the line of sight) and injects the image tothe appropriate waveguide considering the virtual image focus at thatregion).

Each of the light projecting units 210 a, 210 b, 210 c has an opticalprofile (different focal parameters across the FOV) such that, dependingon the light directing unit(s) being selected for operation in theimaging session, the respective light projecting units (i.e. those withwhich both the augmented-image light and real-image light interact)affect light propagation through the system. To this end, the opticalprofiles of the light projecting units 240B′, 240B″, 240B′″, 240C areconfigured such that interaction of the augmented-image light with therespective light projecting units provides a desired effect (focaldistance change), while interaction of the real-image light with therespective light projecting units on its way through the system does notinduce any focal distance change.

Thus, in the example of FIG. 15, light directing units (waveguides) 210a, 210 b, 210 c form together the light directing device 210, and lightprojecting units (lenses having different focal parameters/optical powerprofiles across the fixed FOV) 240B′, 240B″, 240B′″, 240C form togetherthe optical projecting device 240. The combination of some of the unitsof the optical projecting device 240 forming the above-describedaugmented image projecting device and real image projecting device maybe different in various imaging sessions. Here, at least two of thelenses are progressive lenses. Thus, a plurality of virtual focal planesFPa, FPb and FPc may be generated by the light projecting unitsoperating as the augmented image projecting units and the waveguides,and the real-image projecting unit(s) (lens(es)), e.g. 240C,compensate(s) for real world aberrations. The orientation of virtualfocal planes FPa, FPb and FPc can be arbitrarily modified according tothe augmented image affecting progressive lenses 240B′, 240B″, 240B′″.

It should be understood that in the configuration of FIG. 15, theoptical power profiles of all the light projecting units (lenses) areconfigured to provide that, selectively, optical effect (focal change)of one or more of them is compensated by one or more others, such thatthe lens(es) of the augmented image projecting unit in a specificsession and lenses of the real image projecting unit in said sessionshould be configured to compensate for the real-image light modificationinduced by the augmented image projecting unit.

More specifically, for the example of FIG. 15, lens 240C is configuredto apply a compensating/opposite effect for the effect induced by lenses240B′, 240B″ and 240B′″ (for the case only waveguide 210 a is inoperation); lenses 240B′ and 240C are configured to compensate for thereal-image modification induced by lenses 240B″ and 240B′″ (e.g. onlywaveguide 210 b is in operation), and lenses 240C, 240B′, 240B″ areconfigured to compensate for effect of lens 240B′″ (only waveguide 210Cis in operation).

Thus, the present invention provides a novel solution for configurationand operation of an optical system for use in an augmented realitysystem (such as see-through near-eye display system). The technique ofthe present invention enables the use of the optical system having afixed field of view, while providing for required focal distance changeacross said field of view being applied to the augmented image lightand/or real image light being projected onto the image plane (eyebox).

The invention claimed is:
 1. A binocular augmented reality (AR) displayfor providing a projected image superimposed on a view of an externalscene for viewing by eyes of a viewer, the binocular AR displaycomprising a right-eye display and a left-eye display each comprising:(a) a light transmitting waveguide having a pair of parallel majorexternal surfaces; (b) an image projector configured to project imagelight corresponding to a collimated image, said image projector beingoptically coupled to said waveguide so as to introduce the image lightinto said waveguide so as to propagate by internal reflection at saidmajor external surfaces; (c) a coupling-out arrangement associated witha coupling-out region of said waveguide for progressively coupling outthe image light towards the eye of the viewer, the coupled-out imagelight having a field of view including an upper region of the field ofview and a lower region of the field of view; and (d) a multifocalreal-image lens deployed between said waveguide and the external scene,said multifocal real-image lens having smoothly or discretely varyingfocus across the field of view such that said real-image lens has apositive optical power in a region aligned with a line of sight of theeye of the viewer when viewing the lower region of the field of viewthat is greater than an optical power of said real-image lens in aregion aligned with a line of sight of the eye of the viewer whenviewing the upper region of the field of view, wherein said imageprojectors of said right-eye display and said left-eye display projectthe projected image with a continuous change in convergencecorresponding to an apparent change in a focal distance of the projectedimage between the upper region and the lower region of the field ofview.
 2. The binocular AR display of claim 1, wherein said real-imagelens of each of said right-eye display and said left-eye display is aprogressive lens having a smoothly varying focus across the field ofview.
 3. The binocular AR display of claim 1, wherein said real-imagelens of each of said right-eye display and said left-eye display hasdiscrete regions with differing focal parameters.
 4. The binocular ARdisplay of claim 1, wherein each of said right-eye display and saidleft-eye display further comprises a multifocal augmented-image lensdeployed between said waveguide and the eye of the viewer, saidmultifocal augmented-image lens having smoothly or discretely varyingfocus across the field of view such that said augmented-image lens has anegative optical power in a region aligned with a line of sight of theeye of the viewer when viewing the lower region of the field of viewthat is greater than an optical power of said augmented-image lens in aregion aligned with a line of sight of the eye of the viewer whenviewing the upper region of the field of view.
 5. The binocular ARdisplay of claim 4, wherein each region of said augmented-image lens hasan optical power which substantially cancels out with an optical powerof a corresponding region of said varifocal or multifocal real-imagelens.
 6. The binocular AR display of claim 4, wherein said real-imagelens and said augmented-image lens of each of said right-eye display andsaid left-eye display both have a smoothly varying focus across thefield of view.
 7. The AR display of claim 4, wherein said real-imagelens and said augmented-image lens of each of said right-eye display andsaid left-eye display both have discrete regions with differing focalparameters.